1. Field of the Invention
The present invention relates to a media stripper, and a fixing device and an image forming apparatus employing the same, and more particularly, to a media stripper for use with a pair of rotary members disposed opposite each other to form a nip therebetween, and a fixing device and an electrophotographic image forming apparatus, such as a photocopier, facsimile machine, printer, plotter, or multifunctional machine, employing such a media stripper.
2. Description of the Background Art
In electrophotographic image forming apparatuses, such as photocopiers, facsimile machines, printers, plotters, or multifunctional machines incorporating several of those imaging functions, an image is formed by attracting toner particles to a photoconductive surface for subsequent transfer to a recording medium such as a sheet of paper. After transfer, the imaging process is followed by a fixing process using a fixing device, which permanently fixes the toner image in place on the recording medium by melting and settling the toner with heat and pressure.
Various types of fixing devices are known in the art, most of which employ a pair of generally cylindrical looped belts or rollers, one being heated for fusing toner (“fuser member”) and the other being pressed against the heated one (“pressure member”), which together form a heated area of contact called a fixing nip through which a recording medium is passed to fix a toner image onto the medium under heat and pressure.
One such fixing device includes a multi-roller, belt-based fuser assembly that employs an endless, flexible fuser belt entrained around multiple rollers, one of which is equipped with an internal heater, such as a radiant halogen heater, to heat the length of the fuser belt through contact with the heated roller. The fuser belt is paired with a pressure roller pressed against the outer surface of the fuser belt to form a fixing nip therebetween, at which a toner image is fixed in place with heat from the fuser belt and pressure from the pressure roller.
Owing to the fuser belt which exhibits a relatively low heat capacity and therefore can be swiftly heated, the belt-based fuser assembly eliminates the need for keeping the heater in a sufficiently heated state when idle, resulting in shorter start-up time and smaller amounts of energy wasted during standby, as well as a relatively compact size of the fuser assembly.
One important factor that determines imaging quality of a fixing device is the ability to properly convey a recording medium through the fixing nip without causing the recording medium to wrap around the rotary fixing member. Media wraparound occurs where the toner image heated through the fixing nip becomes sticky and thus adheres to the surface of the fixing member upon exiting the fixing nip. If not corrected, a recording medium wrapping around the fixing member would cause jam or other conveyance failure in the fixing nip.
For obtaining a fixing process with high immunity against media wraparound and concomitant conveyance failure, a fixing device may use a fuser roller or belt coated with a release agent such as fluorine resin where it contacts a heated, sticky toner image in the fixing nip, while equipped with a media stripping mechanism that allows a recording medium to properly separate from the fuser member at the exit of the fixing nip.
For example, in multi-color printing, a non-contact media stripping mechanism is used to strip a recording medium without touching a fuser roller, which often includes a cylindrical body covered by an outer elastic layer of silicone rubber or the like with a coating of oil or fluorine resin deposited thereon. Using the non-contact media stripper prevents the rubber-covered fuser member from damage due to continuous contact with the media stripping mechanism, which would otherwise result in streaks or other imperfections in a resulting image.
One example of such non-contact media stripper is a stripping plate having a thin-edged, wedge-shaped configuration with its thin operating edge directed toward a fuser member to engage a leading edge of a recording medium to strip it off the fuser member. The stripping plate may be provided with a flange or positioning mechanism, such as one that can contact the fuser member outboard of a maximum compatible width of recording medium, so as to maintain the operating edge in position spaced apart from the rotary member. Maintaining a spacing or gap between the stripping mechanism and the fuser member prevents damage to the fuser member as well as undesired offset or re-transfer of toner adherent, if any, from the stripping mechanism to the fuser member to potentially smear and degrade a resulting image.